Blood cells, such as stem cells, blood progenitors, red blood cells and all major types of white blood cells, can be effectively mobilized by exercise. Therefore, exercise can affect immunity in a variety of ways. For example, regular, moderate-intensity exercise can help protect people against some diseases, particularly those that involve the upper respiratory track (like colds). However, too much exercise can have the opposite effect and reduce immunity. There is a need in the art for notifying a person about how much exercise is enough, when exercise is appropriate and when it's not, which types of exercise are appropriate for their particular situation, and other exercise-immunity related information. There is also a need in the art for personalizing an immune-affecting activity recommendation based on a person's intrinsic characteristics as well as quantified variable personal traits.